As shown in FIG. 6, a conventional muffler installation structure for compressors includes an end plate member 150 fitted to an opening end of a cylinder body 121, a cup-shaped muffler 140 fitted to the end plate member 150, and a fixing member 135 for fixing the muffler 140 to the end plate member 150 (see, e.g., JP 6-2689 A).
The muffler 140 has a peripheral wall 141 fitted to an outer peripheral surface 151b of a body portion 151 of the end plate member 150. In a state before the muffler 140 is fitted to the end plate member 150, the outer peripheral surface 151b of the body portion 151 of the end plate member 150 is shaped into a generally perfect circle as viewed in the axial direction while an inner peripheral surface 141a of the peripheral wall 141 of the muffler 140 is shaped into a generally perfect circle as viewed in the axial direction.
Then, compressed gas in a cylinder chamber 122 of the cylinder body 121 flows inward of the muffler 140 through a discharge hole 151a of the body portion 151 of the end plate member 150, and flows outward of the muffler 140 through a gap S between a hole portion 142a at a center of the muffler 140 and a boss portion 152 of the end plate member 150.
In this case, there is a need for ensuring sealability between the muffler 140 and the end plate member 150. If the sealability between the muffler 140 and the end plate member 150 cannot be ensured, there are issues (a), (b) and (c) as shown below.                (a) Gas leaks from contact sites between the muffler and the end plate member, causing lubricating oil present inside the compressor to blow up.        (b) Pulsated gas leaks from the contact sites between the muffler and the end plate member, causing occurrence of noise and reduction of the muffling effect.        (c) The contact between the muffler and the end plate member becomes insufficient, so that natural vibrations of the muffler itself are more likely to be excited, causing occurrence of noise.        
However, in the prior-art muffler installation structure for compressors described above, since the outer peripheral surface 151b of the body portion 151 of the end plate member 150 is shaped into a generally perfect circle as viewed in the axial direction and since the inner peripheral surface 141a of the peripheral wall 141 of the muffler 140 is shaped into a generally perfect circle as viewed in the axial direction, there is a need that the diameter of the generally perfect circle of the inner peripheral surface 141a of the peripheral wall 141 of the muffler 140 be set close to the diameter of the generally perfect circle of the outer peripheral surface 151b of the body portion 151 of the end plate member 150 in order to ensure the sealability between the muffler 140 and the end plate member 150. As a result, there are issues (d) and (e) as shown below.                (d) Compressive load on the end plate member due to elastic deformation of the muffler becomes larger, making it difficult to assemble the muffler and the end plate member together.        (e) Compressive load on the end plate member due to elastic deformation of the muffler becomes larger, causing occurrence of strain to the end plate member so that the assembling accuracy between the muffler and the end plate member degrades.        
Thus, the prior-art muffler installation structure for compressors described above is incapable of satisfying improvement of the sealability, improvement of the muffling effect, facilitation of the assembly and improvement of the assembling accuracy at the same time.